Most of us will come into contact with copper every day via the predominantly copper piping in most houses, and normally it’s harmless at these low levels.Potters, however, deal in far greater quantities and in forms that are much more likely to result in toxic overdose.So while we may assume copper is harmless, it still needs to be treated with caution and respect.
Of particular interest to potters, copper has the effect of increasing solubility of glazes when used with lead, rendering otherwise functionalware-safe glazes potentially toxic.Lead should be avoided for all functionalware regardless, but it’s important to recognise that unexpected and adverse chemical reactions can occur with particular colourant combinations.
On its own, Copper Carbonate dust can cause sudden and significant eye irritation and conjunctival inflammation, although the effects pass quickly and seemly without permanent damage once the eye is rinsed.Exposure to skin can cause irritation, itchiness, dermatitis, eczema and hypersensitivity.
Inhalation of the dust or firing fumes has been known to cause ‘Metal fume fever’ with flu-like symptoms of chills, nausea, aches, weakness, fever and respiratory irritation.Although instances of this through kiln fumes are uncommon beneath cone 8, before the Copper volatilises.
Inhalation or ingestion has been implicated in a possible increased risk of pancreatic cancer, dysrhythmia and coronary artery disease.In addition, has been believed to cause anaemia, severe nausea, abdominal pain, a burning of the oesophageal or gastric tissue, vomiting, hypotension, gastrointestinal bleeding with associated hematemesis and melena.Large levels of ingestion may result in hepatic and renal failure, coma, shock and subsequent death, although the estimated lethal dose for an adult is between 10 – 20g, so that amount is unlikely to be ingested accidentally.
Copper is volatile at cone 8 and above and therefore can spit and jump from pot to pot, marring nearby pieces.Copper Carbonate is particularly prone to this due to producing more gas than Oxide as it decomposes, which results in a predilection towards pinholes and blisters.It gives less intense colouration than Copper Oxide due to a lower percentage of copper, and appears more uniform in coverage.Different firing rates, lengths and soaks can affect the particular shade of green in a non-reduction firing, so firing fast with brief or no soaks are generally recommended.The use of Copper in a glaze may increase crazing due to its high thermal expansion.Above approximately 5% Copper content, the colour will begin to move to black, and at more than 7% metallic and graphite effects will begin to appear.
Alkalising agent = Turquoise Lead = Greens (Note: Increased toxicity, not for functionalware) Barium = Blues and Blue-Greens Fluoride = Blue-Greens Potassium Oxide = Yellow-Greens Tin = Red in reduction (with low alumina, high alkali) and Blue in oxidisation